AST 114 – Spring 2005
Determining Our Position in the Milky Way
DETERMINING OUR POSITION IN THE MILKY WAY
What will you learn in this Lab?
What is the Milky Way? How was our location in it initially determined? How is the Milky
Way oriented with respect to the Solar System? Is the Milky Way uniformly populated with
stars, as we see it?
What do I need to bring to the Class with me to do this Lab?
For this lab you will need:
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A copy of this lab script
A pencil
Your star charts
Audubon Field Guide
Introduction:
The purpose of this lab is to chart the Milky Way from the light polluted skies of Tempe. In
general, seeing the Milky Way with the naked eye requires a clear, dark sky (e.g.
Flagstaff) – a situation seldom found near a large city. Tonight you will be investigating
the Milky Way in two ways – completing an indoor exercise using compiled data and
confirming what you have learned from the indoor part of the lab by using binoculars to
look at star fields in different regions of the sky.
PART I: Indoor Exercise
Exercise
This exercise will help you visualize the process of taking observations and plotting them
on a map. Imagine that you are inside a large cloud of fireflies. This cloud of insects is
analogous to the cloud of stars that you see dotting the night sky. Discuss among
yourselves what you would see if you were in the following scenarios. Take some notes
since these will be useful for the following exercises. Also sketch the distribution of
fireflies on the maps next to each scenario. The maps are printed flat, but like maps of the
world they represent a spherical surface – imagine an orange peel cut off the orange and
laid flat.
© 2005 Arizona State University
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Determining Our Position in the Milky Way
1. You are at the center of a uniform sphere of fireflies:
2. You are at the edge of a uniform sphere of fireflies:
3. You are at the center of a very thin disk of fireflies:
4. You are at the edge of a very thin disk of fireflies:
Now we are going to create a map that shows the distribution of some of the different
types of celestial objects visible in the night sky – globular clusters, spiral galaxies, open
clusters, gaseous nebulae. At the end of the lab script you will find a list of constellations
within which certain numbers of each type of object can be found. The number count for
each type is listed. With that you will find a map of the sky with the constellations
delineated. The Milky Way is already shown. Using the table, choose a symbol for each
type of object, and mark the appropriate number of object/symbols within each
constellations boundary. Follow this procedure:
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Mark the location of each object on the map toward the center of the zone that
defines the constellation. Make the symbols dark enough that you can see them
through the paper.
Use a different symbol for each class of object.
© 2005 Arizona State University
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Determining Our Position in the Milky Way
Lightly color the Zodiacal constellations.
Cut out the map carefully.
Construct the globe using tape
Note: The globe you’ve made is inside out. We would typically view the “celestial globe”
from the inside, but in this case we’ve taken a map of the sky and made a globe out of it
with the inside on the outside. This means that the order of the constellations on the
outside of the globe is reversed from what it should be.
Questions for Part I
1. Examine the globe that you’ve built and pay particular attention to each class of
object. Make a clear statement about the distribution of Globular Clusters, Spiral
Galaxies, Open Clusters and Gaseous Nebulae. Describe what you see and be as
detailed as you can in describing the distributions. Make particular reference to the
path of the Milky Way.
2. Compare the distributions you observed for each of the types of objects with the
patterns you generated for the fireflies. Do any of them match? Do any of them
partly resemble each other? What does this tell you about the real spatial
distribution of each type of object relative to the Earth?
© 2005 Arizona State University
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Determining Our Position in the Milky Way
3. Now consider the overall structure of our Galaxy, as represented by the Milky Way
on your globe. What do the answers for question 2 tell you about the distribution
of the various types of objects within the Galaxy? Be specific for each type of
object – globular clusters, spiral galaxies, open clusters, emission nebulae.
4. Using your answers now draw a sketch of the Galaxy showing where in the
structure each type of object can typically be found. Be sure to add labels to make
the sketch clear.
PART II: Outdoor Exercise
Based on your model of the cloud of fireflies and your description of the Milky Way
structure that you determined in part I, you are able to make predictions as to the
distribution of stars on the sky and the shapes of some galaxies, like our own. Predict the
answers to the following questions, based on what you've learned.
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Should you see a higher density of stars away from the Milky Way or within the
Milky Way?
Are all galaxies spherical in nature or should some galaxies look like disks?
Now you will go to outside and make some observations to test your predictions. With the
help of your TA, you will use two pair of binoculars to look at two locations on the sky to
test your prediction about the density of stars.
Two locations:
Location 1: located in constellation _______________________
Location 2: located in constellation _______________________
© 2005 Arizona State University
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Determining Our Position in the Milky Way
Questions for Part II
1. Inspect the two constellations by eye. Which location has the higher density of
stars?
2. You determined a constellation that had a high density of stars. Look at your
constellation model from Part I. Does your outdoor observation match a
constellation near or within the Milky Way? Does your observation match your
prediction?
PART III – Additional Questions
1. Where in the Milky Way are we? How can you tell?
2. What is the approximate shape of the Milky Way? Be precise in this description.
© 2005 Arizona State University
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3. Look at your star charts or starwheel and answer the following questions:
a. Do the brighter stars correlate with the location of the Milky Way? What does this
tell you about the distance of the brighter stars compared to the size of the Milky
Way?
b. Are there any dense concentrations of stars away from the Milky Way?
4. Through which constellations does the Milky Way pass? How is it oriented with
respect to the ecliptic (zodiacal constellations)?
Conclusion:
© 2005 Arizona State University
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Constellation
Cepheus
Pegasus
Aquarius
Capricornus
Grus
Draco
Cygnus
Vulpecula
Aquila
Sagittarius
Telescopium
Hercules
Ophiuchus
Scorpius
Lupus
Norma
Ursa Majoris
Canes Venatici
Bootes
Coma Berenices
Virgo
Centaurus
Leo
Hydra
Camelopardalis
Monoceros
Canis Major
Puppis
Perseus
Taurus
Orion
Eridanus
Dorado
Cassiopeia
Andromeda
Triangulum
Pisces
Cetus
Fornax
Sculptor
Determining Our Position in the Milky Way
# Globulars
# Spirals
4
1
4
2
© 2005 Arizona State University
# Opens
3
# Gaseous
6
7
6
4
2
3
2
5
3
2
20
8
4
8
6
2
4
1
1
4
6
5
4
3
3
8
3
1
5
3
6
8
7
16
10
2
3
2
2
1
3
1
12
11
5
8
2
4
8
4
4
7
3
7
2
5
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© 2005 Arizona State University
Determining Our Position in the Milky Way
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